Process for the solution mining of potassium compounds



Patented Aug. 3, 1954 PROCESS FOR THE SOLUTION MINING OF POTASSIUM COMPOUNDS Walter M. Cross, .l'r., Kansas City,

to Kansas City Testing Laboratory,

Mo., assignor Kansas City, Mo., a corporation of Missouri No Drawing. Application June 30, 1948, Serial No. 36,271

3 Claims.

1 This invention relates to an improved process of recovering potassium salts from brines and ores. More particularly, this process pertains to a method of eliminating the interference of certain salts which may periodically be present in solution mining when an ore variant in potassium concentration is mined.

Present methods of mining potash are akin to shaft, room and pillar type of mining, or of the solution type, several of which methods are described in Patents No. 2,161,800 issued June 13, 1939, and No. 2,331,890, issued October 19, 1943, granted to Dr. Roy Cross and assigned to the assignee of the present application.

In solution mining of potash superheated liquor may be introduced to a potash bed or beds, thereby dissolving a mixture of salts containing potash. The salt solution is subsequently cooled, whereby potash is deposited out from the saturated salt liquor. In another method of solution mining substantially all of the potash salts are removed from salt deposits of potassium chloride and sodium chloride, leaving most of the sodium chloride in situ when a superheated mother liquor is used which is a solution substantially saturated with respect to both sodium chloride and potassium chloride. This method proceeds on the theory that solubility of potash salts is proportional to increase of the temperature of the dissolving medium. The solubility of the potash salts is greater than some other salts; sodium salts for example. When a superheated solution is introduced greater quantities of potash are dissolved and less amounts of other salts. Solutions of higher potash concentration are obtained by solutions which will take up only potash salts. Accordingly, hot solutions which are already saturated with undesirable salts are employed circulated into potash deposits. An equilibrium of solution between potash salts and other salts occurs, and the solution takes up potash salts since it is already saturated as to the undesirable salts found in the deposit.

A problem encountered in either of the above described solution mining methods has occurred where the potash beds so mined contain either magnesium or sulphate compounds or both. Salts of this type serve to saturate the dissolving mother liquor to the exclusion of the potash salts. It therefore becomes necessary when these salts are encountered in the mining operation to raise the saturation ability of potash in the brine or other solution introduced so as to dissolve the salt bed so that less water is required to be evaporated in the recovery of each potash unit.

F duced in preference to Evaporation is an expensive operation and a means for reducing the proportions of such operation decreases commensurately with the cost of over-all mining operation. Hence, the expense involved for mining a unit of potash, be it pound, barrel or ton, is also decreased.

I have discovered that the depressant effect of magnesium and sulphate salts may be removed by changing such salts to a hydroxyl form. Such change serves to render magnesium or sulphate ions either relatively insoluble or inactive as to the inhibition of the solubility of potassium.

The novelty in the method herewith described is that in above ground operations upon crushed ore, the ore in leaching operations is under control, and the potash content of the ore is of sufficent concentration to permit excellent potash saturation. But in operating under ground, it is impossible to choose the type of ore for operation, and in the case where the ore is not rich, the law of mass reaction becomes operative. This is of great consternation. Thus, as an example, where sodium chloride is present in the ore beds, it goes into solution in the mother liquor introthe potash salts. Variant temperature control of the mother liquor only indicates that at a higher temperature, more salt is taken up. Though in a pure water solution the solubility of potassium chloride is greater than that of sodium chloride, in a solution of water with a mixture of the two salts the rate of solution of sodium chloride is faster. It becomes necessary, therefore, to eliminate as many fac tors which tend to depress the solubility of the potash salts, so as to maintain an operable potassium chloride-sodium chloride ratio.

In a typical well in a potash bed the following may be descriptive of my operation: Normally, a value of 1% pounds potassium chloride to one gallon brine is obtained. In a typical instance this value may fall to 0.3 lb./gal. At this point the particular ore reaches an equilibrium. The underground pool is estimated at barrels volume. In order to raise the saturation of potash in the brine, I treat the brine with sodium hydroxide in order to convert magnesium chloride, for example, to magnesium hydroxide. This raises the potassium chloride concentration, and in one instance, specifically raised the value of concentration of potassium chloride from 0.3 lb./gal. to 0.5 1b./gal. In point of time this saturation increase is immediate; in typical operation an increase of saturation of 0.2 lb./gal. is obtained in one hour. In other instances a saturation figure of less than 0.3 lb./gal. has been raised to 0.6 lb./gal. Higher concentration is imsaid liquor to between 8 and 10 thereby to repress portant since less evaporation is required to rethe solubility of the magnesium and sulfate ions cover potash with consequent decrease in operatin said liquor, withdrawing a portion of said body ing costs. of liquor rich in potassium compounds from said Treatment with calcium hydroxide yields 5 deposits, reducing the concentration of potasequally good results. Both agents se ve chiefly sium compounds therein by separating a" portion to convert magnesium chloride into magnesium of said potassium compounds, and returning the hydroxide, a compound of relative insolubility. residual lean liquor to said circulating body.

Where calcium sulphate is present it is con- 2. A cyclic process for the solution mining of verted to calcium hydroxide. Reagents which 10 potassium compounds from underground water are suitable for such conversion may be caustic mm deposits containing potassium magnesp soda or lime, the latter being more Su a l 106- um and sulfate ions which comprises circulating us of s e p s In a tu e f sa t a body of aqueous solvent liquor unsaturated mp s n p sh and sal s c n in ng he hywith respect to potassium compounds into cond yl ion, the hydroXyl i is of little p s- I tact with said deposits, adding a quantity of an sant effect, whereas the soluble magnesium and inorganic alkaline compound from the group p a e ions serve o a e difi y by readily consisting of sodium hydroxide, soda ash, calcis n in o sol tion and by spl in he irum hydroxide, lime and trisodiumphosphate able potassium iOHS- Calcium Sulphate y e sufficient to raise the pH of said liquor to between eliminted by using sodaash or a chemical of the a and thereby to repress the solubility of the tri-sodium phosphate type. magnesium and sulfate ions in said liquor, withh S method ma -S S l mining Possible drawing a portion of said body of liquor rich without superhe t g e m e quor used to in potassium compounds from said deposits, redissolve the potash beds. Cold water will serve ducing the concentration of potassium comto yield the results as above described. pounds therein by separating a portion of said The conversion of undesirable ions into a nonpotassium compounds and returning the residual interfering form is operative when the akaline l i or t aid circulating body.

reagent i in i i nt qu n i y to k p he 3. A cyclic process for the solution mining of Solving brine at a pH of 8-0 to 10-0- eating the potassium compounds from underground water mother liquor 80 as o impart iJhiS P y be soluble deposits containing potassium, magnesione n ad e f actual Operations 0r Concllrum and sulfate ions which comprises circulating rent with the p p Operation after the a body of aqueous solvent liquor unsaturated mining y le is in operation. Since there is no with respect to potassium compounds into conoritical phase in the Ope When the alkar tact with said deposits, adding a quantity of lime linity must be imparted, t process herein sufilcient to raise the pH of said liquor to between scribed may be undertaken in all solution min- 8 and 10 thereby to repress the solubility of the s p ss s t f r or cu r y mpl y magnesium and sulfate ions in said liquor, With- There is no limitation upon use of the alkaline drawing ortion of said body of liquor rich material with respect to temperature. Therein potassium compounds from said deposits, re-

fo e, the S l o s ed in my mining methOdS 4o ducing the concentration of potassium comd c in y patents already issued y 108 pounds therein by separating a portion of said treated to a point of alkalinity so as to avoid the ta si m compounds, and returning the residinterference of the kind described herein. An ,1 l liquor to said, circulating body. optimum range of operation for efiecting the benents of this method may be obtained by References'cited in the file of this patent bringing thfi mother liquor to a pH Of 8 t0 10.

What I claim is as follows:

1. A cyclic process for the solution mining of Number Name Date potassium compounds from underground water 1,466,352 Dolbear 1923 soluble deposits containing potassium, magnesi- 11812397 Ransom June 1 um and sulfate ions which comprises circulating 1,820,160 Rilsberg 25, 1931 a body of aqueous solvent liquor unsaturated 2029623 Kircher et a1 4, 1936 with respect to potassium compounds into con- 233L890 Q1055 19, 1943 tact with said deposits, adding a quantity of 23881109 Plke Oct 30) 1945 sodium hydroxide sufiicient to raise the pH of 2,404,550 Thomsen July 23, 1946 

1. A CYCLIC PROCESS FOR THE SOLUTION MINING OF POTASSIUM COMPOUNDS FROM UNDERGROUND WATER SOLUBLE DEPOSITS CONTAINING POTASSIUM, MAGNESIUM AND SULFATE IONS WHICH COMPRISES CIRCULATING A BODY OF AQUEOUS SOLVENT LILQUOR UNSATURATED WITH RESPECT TO POTASSIUM COMPOUNDS INTO CONTACT WITH SAID DEPOSITS, ADDING A QUANTITY OF SODIUM HYDROXIDE SUFFICIENT TO RAISE THE PH OF SAID LIQUOR TO BETWEEN 8 AND 10 THEREBY TO REPRES THE SOLUBILITY OF THE MAGNESIUM AND SULFATE IONS IN SAID LIQUOR, WITHDRAWING A PORTION OF SAID BODY OF LIQUOR RICH IN POTASSIUM COMPOUNDS FROM SAID DEPOSITS, REDUCING THE CONCENTRATION OF POTASSIUM COMPOUNDS THEREIN BY SEPARATING A PORTION OF SAID POTASSIUM COMPOUNDS, AND RETURNING THE RESIDUAL LEAN LIQUOR TO SAID CIRCULATING BODY. 